So-called microlithographic projection exposure apparatuses are usually used for producing microstructured components such as e.g. integrated circuits or LCDs. In these apparatuses, the image of a lithography mask (=reticle) is projected onto a substrate (e.g. a silicon wafer) coated with a light-sensitive layer (photoresist) via a projection lens in order to transfer the mask structures onto the light-sensitive coating of the substrate. In the process, the lithography mask is displaced laterally with the aid of a so-called reticle stage in order also to successively image relatively large structures. By way of subsequent developing, etching and doping process, cost-effective large quantities of microstructured components may be achieved in this manner.
Here, the quality of the lithography mask plays a decisive role since an error in the mask structure propagates into the components emerging therefrom.
Therefore, complicated measurement apparatuses were developed, by which the mask structures may be measured after and during the production process of the lithography masks.